Power systems typically comprise a plurality of components, such as one or more power generation source, drives and energy storage modules. These components are typically interconnected by means of a busbar system in which currents can flow for providing power to one or more loads connected to the power system.
At some point a fault, such as a short circuit will inevitably occur in the power system, either in the busbar system, in one of the components of the system, or in a load. In case of a fault, it is important to isolate the fault from the healthy part of the system such that normal power provision can be continued by means of the healthy part, and for protecting the healthy parts from being damaged. For this purpose, a protection system is typically included in the power system.
A protection system arranged to handle faults in a power system typically comprise monitoring equipment arranged to monitor electrical parameters such as currents in the power system, and circuit breakers controlled by the monitoring equipment. The circuit breakers are arranged in such a way in the power system that selective fault isolation can be obtained in case of a fault.
US2003/0071633 discloses an AC electric power supply network (sic) comprising a bus system and feeders for distributing power to remote locations. Between each line and the bus is provided a breaker.
EP1843443 discloses a DC electrical current busbar associated with electrical load circuits and devices as well as sources requires protection. In order to provide such protection Kirchoff's laws are utilised such that electrical current values are substantially simultaneously taken and summed in order to identify deviations from expected differential threshold values. Upon detection of such deviations and generally as a result of a number of successive deviations an electrical isolation device is utilised in order to isolate electrical current to the busbar. The data set of electrical current values can be utilised in order to provide a back up protection system for individual electrical load devices and circuits, by similar comparison with expected values for those devices and circuits.
GB1151457 discloses a safety device for inverters supplying asynchronous motors. In the background section of this disclosure, it is mentioned that “in the case of faults in the inverter equipment, representing a short circuit of the d.c. circuit, the smoothing capacitor is discharged through the short circuit. Since the smoothing capacitor has a high capacitance, the discharge current may reach very high values. This causes the response of the fuses connected upstream of the current converters in known circuits. In consequence, the converters are disconnected from the short circuit.”
WO2011/141052 discloses a plant for transmitting electric power comprises a high voltage DC line, a DC breaker connected in series with the DC line and configured to break a fault current upon occurrence of a fault on said DC line, means configured to detect occurrence of a fault current, a control unit configured to control a said DC breaker for protecting equipment connected to the DC line upon occurrence of a the fault current and means configured to dissipate energy stored in a faulty current path of the DC line between said location and these means upon occurrence of a said fault to the moment of said control of said DC breaker. The energy dissipating means comprises a series connection of an energy consuming braking resistor and a free-wheeling rectifying member connected between ground and said DC line to conduct current while forming a free-wheeling path therethrough upon said control of said DC breaker upon occurrence of a said fault.
Existing protection systems can however in some applications be both very expensive and space consuming.